This invention relates to a circuit arrangement for starting and operating a gas discharge lamp with a current of higher frequency, and provided with an electronic ballast unit which is to be connected to an input d.c. voltage source and comprises an electronic switching element which is controlled by a control device and is connected in series with an inductive element which is acted upon by the lamp current and from which a voltage can be derived, which is fed as a d.c. supply voltage to the control device through a rectifier and a smoothing capacitor. A current of higher frequency is to be understood to mean an alternating current having a frequency between 10 and 500 kHz, preferably between 20 and 150 kHz.
Circuit arrangements of this kind are described in DE OS 25 46 760 and DE OS 31 11 561. There the d.c. supply voltage is produced by means of a tapping or a secondary winding of an inductive element which is already a part of the electronic ballast unit. However, when the d.c. supply voltage is produced in this manner, the electronic switching element can be switched at higher frequency in general only if a d.c. present. For this reason, in the known circuit arrangements, a starting circuit is used which ensures that the control electrode of the electronic switching element is acted upon &from the rectified mains voltage through resistors or diodes and capacitors by a d.c. supply voltage, which initiates the step of switching the electronic switching element at higher frequency. This has the disadvantage that additional elements are required, which otherwise do not fulfill any function and in which moreover losses occur. Besides, especially in circuit arrangements having an electronic control device for current limitation, the problem can arise that at the instant at which the electronic switching element is switched on through the starting circuit the control device has not yet been sufficiently supplied with voltage. Consequently, the current limitation function of the control device may not yet be in operation so that the switching element can be destroyed by excess currents.
For this reason, it is known from EU-OS 00 59 053 to charge directly the smoothing capacitor with the d.c. supply voltage through a starting circuit in the form of a thyristor, as a result of which the electronic switching elements are not switched on until the control device is also operative. Also in this case, additional elements are required, which otherwise do not fulfil any function.